The Notch family of proteins is comprised of four highly conserved membrane receptors. At least three of these proteins, Notch1, Notch2 and Notch3, are expressed at various times during lymphoid development. Under normal circumstances, Notch expression directs the development of the T cell lineage. Aberrant Notch expression results in T lymphoid tumors suggesting the expression of this gene can participate in oncogenic transformation. Data from our last funding period demonstrated that Notch is activated by signals through the TCR. We demonstrated that Notch is required for NF-kB activity through physical interactions between Notch and NF-kB family members. We also showed that Notch is required for TH1 function. Lastly we demonstrated that Notch regulates cell cycle progression in T cells through activation of cyclin D3. The current application proposes three aims to expand on our observations over the past four years. In this application, we propose the hypothesis that differential expression of Notch ligands on APCs have various functional consequences in driving CD4+T cell responses and experiments designed to test this hypothesis are proposed. In particular, we predict from our preliminary data as well as published data from others that the Notch ligand, DLL1 activates Notch signaling in CD4+ T cells while Jagged-1 does not activate Notch in this cell population. Furthermore we predict that this differential activation of Notch is responsible for the polarization of TH1 cells. Aim 1 will ask how TCR signaling induces the activation of Notch and will explore the role of ligand in this process. Aim 2 will ask how Notch regulates the Carma1/Bcl10/Malt1 (CBM) complex and present experiments to further determine how Notch regulates NF-kB. Aim 3 will explore the hypothesis that differential expression of Notch ligands on APCs has various functional consequences in driving CD4+T cell responses. In particular, Aim 3 will test the hypothesis that signals through different ligands differentially activate Notch and this results in differential activation of NF-kB which in turn influences polarization to either a TH1 or a TH2 response. PUBLIC HEALTH RELEVANCE: The contributions of this research to human health are numerous. The biological system we investigate;the immune system, is critical to human health and the molecule we study;Notch, is necessary to mount a normal immune response. Equally important is the fact that Notch, when inappropriately expressed, can lead to cancers of the immune system.